1. Field of the Invention
The invention relates in general to door entrances, and more specifically to fire resistant elevator hatchway door entrances.
2. Description of the Prior Art
The walls of a building may be constructed with a certain fire rating, and accordingly, the doors which close openings between the various compartments of the building should be constructed to maintain the integrity of the fire resistive walls. A standard method of fire testing door assemblies, which is set forth under the ASTM designation E152, mounts the doors in a wall enclosing a furnace, with the temperature of the exposed door assembly increasing with time according to a predetermined time-temperature curve. For example, if a 11/2 hour rating is desired, the temperature will be at 1800.degree. F. at the end of the 11/2 hour exposure period. At the end of the exposure period, the door is rapidly cooled with water from a hose stream, the parameters of which are specified according to the fire rating desired and the square feet of exposed door area. One of the conditions for acceptance of horizontal slide-type elevator doors, is that the lap edges of the door panels shall not move from the wall or adjacent panel surfaces sufficiently to develop a separation of more than 27/8 inches (73.0 mm) during the entire classification period, or immediately following the hose stream test.
The side jambs of elevator door and entrance assemblies tend to bow inwardly during such fire and hose tests, with the tendency being exacerbated with increasing door heights.
Dry wall construction, while relatively new in buildings, has rapidly replaced masonry construction. Thus, the fire rated door assemblies should be constructed to obtain the desired rating with dry wall construction. If a door assembly passes the fire test and obtains a fire rating with dry wall construction, it will also be suitable for masonry construction. The reverse may not be true, as masonry construction provides more support for the entrances than dry wall.
While a fire rating is desired for elevator door assemblies, it is essential that the rating be achieved with an economically competitive structure. Thus, it would be desirable to provide a new and improved fire resistant elevator door entrance assembly which is capable of being fire rated using dry wall construction, which is suitable for door heights up to and including 10 feet, and which may be economically manufactured and assembled.